1 Controlling spontaneous emission J-J Greffet Laboratoire Charles Fabry Institut d’Optique, CNRS, Université Paris Sud Palaiseau (France)

2 Lecture 1 Controlling spontaneous emission: nanoantennas and super radiance Lecture 2 Harnessing blackbody radiation

3 Goal of an antenna for single photon emission Electrical Engineering point of view: The source drives the antenna currents The currents radiate Quantum optics point of view: The atom excites the antenna mode The antenna mode has radiative losses How can we get more energy out of one atom ?

4 Example of antenna Chevalet

5 Mühlschlegel et al. Science 308 p 1607 (2005) Optical Nanoantennas

6 Kühn et al. PRL 97, (2006)Anger et al., PRL 96, (2006) Nanoantenna for fluorescence

7 Drexhage Tailoring decay rate

8 Controlling the direction

9 Controlling the lifetime Fermi golden rule :

10 Increasing the decay rate Akselrod et al., Nature Photonics 8, p 835 (2014)

11 Controlling spontaneous emission with a plasmonic resonator Nanoantennas for light emission by inelastic tunneling Scattering by a dense cloud of cold atoms Outline F. BigourdanB. Habert N. Schilder

12 Nanoantennas for light emission by inelastic tunneling Can we overcome quenching ?

13

14 What is the gap plasmon mode ? 500 nm800 nm

15 Emission with a nanocylinder antenna

16 Where is the improvement coming from ?

17 Nanoantenna design rules Chen et al., Phys. Rev. Lett. 108, (2012) Akselrod et al., Nature Nanophotonics 8, p 835 (2014) Bigourdan et al., Opt. Exp. 22, 2337 (2014) Kern et al., arxiv

18 Suppressing blinking of quantum dots Collaboration: B. Dubertret, ESPCI B. Habert

19 Plasmonic nanoresonator B. Ji et al., Nature Nanotechnology 10, p 170 (2015) The gold nanoshell serves as a nanoantenna Collaboration: B Dubertret (LPEM)

B. Ji et al., Nature Nanotechnology 10, p 170 (2015)

21 Colloidal Quantum Dots Blinking Collaboration: B Dubertret (LPEM)

22 Neutral exciton Charged exciton (trion) 160 ns 80 ns 20 ns Decay acceleration B. Ji et al., Nature Nanotechnology 10, p 170 (2015)

23 Is it a Purcell effect ?

24 The gold nanoshell supresses the blinking Neutral exciton Charged exciton (trion) 160 ns 80 ns 20 ns Blinking suppression B. Ji et al., Nature Nanotechnology 10, p 170 (2015)

25 Plasmonic resonator The gold nanoshell increases the stability of the QD: B. Ji et al., Nature Nanotechnology 10, p 170 (2015)

26 Collective effects in light scattering N.J. Schilder, C. Sauvan, J.P. Hugonin, A. Browaeys, Y. Sortais, F. Marquier Laboratoire Charles Fabry, Institut d’Optique, Palaiseau (France)

27 System of interest Dense cloud of ~ atoms Random atom distribution 1 μm ~

28 1.Dense sample: or 1.Dipole energy dominates temperature:  T < 100 μK (  ~ 1 MHz) Laser cooled atomic gases T. Bienaimé et al., PRL 104, (2010) H. Bender et al., PRA (2010) Chalony et al., PRA (2011) Balik et al., PRA 87, (2013) Experiments with large ( ) and optically thick cold samples λ ~ 1 μm  Conditions to observe optical resonant dipole-dipole interactions

29 Spontaneous emission (low excitation regime) Scattering of light (low excitation regime)

30 Spontaneous emission What is the influence of collective effects on the spontaneous emission rate in the presence of strong interactions?

31 Wigner-Weisskopf theory Hamiltonian of the system: Atom-photon coupling constant No rotating Wave Approximation is made in order to keep all interactions mediated by virtual photons ! (by evanescent waves for nanophotonics people). Fixed polarization  + along the cloud axis.

32 Wigner-Weisskopf theory + Choice of the general form of the wavefunction (low excitation) Linear system for the eigenstates

33 Wigner-Weisskopf theory + Choice of the general form of the wavefunction (low excitation) Linear system for the eigenstates Discussion: i) The system is identical to the classical picture ii) The near-field vectorial interactions are essential (and therefore no RWA can be performed). Li et al., PRA 87, (2013)

34 Eigenstates

35 Type 1 and 2

36 Structure of super radiant states

37 Type 3

38 Superradiant polaritonic modes Properties 1. Large decay rate (> 15  0 ) 2. All atoms are excited. 3. Spatial structure accounting for the retardation. 4. There are typically 5 superradiant states among 450 states. Why 5 states ?

39 Superradiant polaritonic modes Properties 1. Large decay rate (> 15  0 ) 2. All atoms are excited. 3. Spatial structure accounting for the retardation. 4. There are typically 5 superradiant states among 450 states. Why 5 states ?

40 Experimental investigations: weak excitation limit F = 1 F = 2 F’ = 3 Δ Laser - cooled 87 Rb atoms T ~ 100  K

41 Scattering in the low excitation regime The positions are generated randomly. The calculation is repeated over an ensemble of random realizations. Both the field and the square of the field are averaged.

42 Role of super radiant modes

43 Coherent and incoherent scattering Light scattering by a suspension of latex beads in water. = mean field (ensemble average)= coherent field= collimated field  E = fluctuating field= incoherent field= diffuse field

44 Coherent and incoherent scattering It can be shown that: In a diagrammatic approach, the effective permittivity is essentially given by the so-called mass-operator. For dense media, the inclusion of recurrent scattering terms is required.

45 Far-field scattering pattern Coherent scatteringIncoherent scattering Most of the light is scattered coherently !

46 Is Clausius Mossotti formula valid ?

47 Order of magnitude analysis Estimate of the permittivity: At resonance:

48 Effective permittivity

49 Structure of super radiant states

50 Controlling spontaneous emission with a plasmonic resonator Nanoantennas for light emission by inelastic tunneling Scattering by a dense cloud of cold atoms